The present relates to an improved nozzle shut-off valve for an injection molding machine. One aspect of the invention also relates to a complete injection molding machine having an improved nozzle shut-off valve. An aspect of the invention is a nozzle shut-off valve having fluid pressure operated pistons at lower ends of the valve elements which are a long pin and short pin cooperatively arranged to block and unblock the plastic injection passageway.
U.S. Pat. No. 3,500,501 issued on Mar. 17, 1970 is the prior art over which the present invention is an improvement. Said U.S. Patent provides a nozzle shut-off device interposed between a nozzle having a plasticizing chamber, the device having therethrough a passageway for molten material and a spool reciprocable to intersect said passageway. The spool also has a passageway and it is capable of communicating with the melt passageway. Ordinarily, the spool travels perpendicular to the melt passageway. Pistons on the ends of the spool are caused to push the spool back and forth as needed by connecting same to a source of fluid pressure. In one position the spool blocks the first passageway and the other position aligns the spool and melt passageways to allow molten plastic material to enter the nozzle.
The present invention affords a different structure which provides manufacturing as well as operational improvements. The desired mode of operation of course is to block and unblock the passageway leading into the nozzle thereby to shut-off or permit flow of molten material. Most succinctly, the structural difference of the present invention employs a long pin and a short pin, both arranged to slide in a passageway that intersects the melt passageway. The pins can be driven towards the melt passageway but are not physically connected to the pistons at their ends. This facilitates assembly by eliminating alignment problems and also improves operation inasmuch as operating conditions such as high temperature and the various axial and pressure forces on the nozzle may create occasional problems.
Thus, in a preferred embodiment, the present invention relates to a nozzle shut-of device for use in an injection molding machine by being interposed between the nozzle and plasticator melt chamber thereof, which device comprises a body having therethrough a first passageway for alignment and communication with said chamber and a passageway formed in said nozzle, and second and third passageways in said body substantially coaxial with each other and on opposite sides of and intersecting said first passageway at a substantially common location; first and second cylinders mounted on said body respectively at that end of said third and second passageways remote from said first passageway; first and second pistons respectively mounted on said first and second cylinders; a long pin reciprocably mounted in said second passageway, of a cross section sufficient to substantially block said second passageway and having a length sufficient to extend from said second piston along said second passageway completely across said first passageway and to enter said third passageway; and a short pin reciprocably mounted in said third passageway, of a cross section sufficient to substantially block said third passageway and having a length sufficient to extend along said third passageway from said first piston but to protrude not more than partly across the first passageway.